The present invention relates to seal-less pump. Particularly it relates to a high pressure multi-stage seal-less pumps not requiring seal member, in which liquid leaks and air suction are prevented.
Hitherto, a multi-stage metallic pump or plastic chemical pump which has required high pressure for transferring liquids such as fresh water or a chemical solution has required a mechanical seal or bearing.
However, especially when liquids such as chemical solutions which are liable to be crystallized or gasified are transferred, many problems arise. For example, sliding parts are worn, or air is collected in the bearing portion, to generate heat, or the shaft is partially worn at contact portions due to eccentricity caused by abnormal wear, causing decentering. Furthermore when a chemical pump is designed for high pressure applications, the increase in the number of impeller stages highlights the reliability of the mechanical seal, and for higher pressures, the mechanical seal must be made precise, using a material high in heat resistance, sliding capability and thermal conduction suitable for the chemical solution concerned. Thus, the pump becomes large, and yet the upper limit of pressure is only about 5 kg/cm.sup.2. It is also difficult to select an appropriate material for the mechanical seal for the respective kinds of chemical solutions.
Some materials resist chemical solutions but are vulnerable to wear. Some resins are low in thermal conductivity and are therefore liable to be deformed. Thus, generally suitable seal materials are not available. Furthermore, since sliding members are always used, the wear of the seal when transporting very pure water has remained a problem.